[en] A LOCA analysis at coldleg of the reactor thermal hydraulic test facility using CATHENA computer code has been completely conducted. The analysis was performed by modeling the reactor thermal hydraulic test loop into generic models of the CATHENA such as PUMP, VALVE, VOLUME, ACCUMULATOR, TANK, RESERVOIR, DISCHARGE, GENERALIZED TANK, and GENHTP. The primary system was simulated at power of 1 MWatt with pressure and mass flow at 15.5 MPa and 9.4 kg/s respectively. At secondary side, feedwater flowed at 15.0 kg/s with temperature of 27 ^oC and pressure of 0.8 MPa. The calculation showed that during steady state the inlet and outlet temperature of test section were 121 ^oC and 146 ^oC. After calculating steady state condition, the calculation was followed by transient calculation. The transient was triggered by pipe break at coldleg with diameter of the break was 2 mm. Due to this break, the pressure decreased dramatically. When the pressure reached 4.2 MPa, the accumulator started supplying water into the system. A moment later, the pump was also tripped because of the continuing pressure drop that reached 4.0 MPa. As a consequence the coolant flow was also dropped At the coolant 40 % of normal flow, the power of heated rods then shut down. The result of calculation showed that during the transient, the maximum coolant temperature was 159 ^oC and the maximum temperature of heated rods was 223 ^oC. Based on these results, it can be concluded that during the transient, the heated rods were not in danger. (author)